1. Field of the Invention
This invention relates to a method of manufacturing a lead ruthenate-containing resistor paste having particularly excellent voltage resistance properties, high resitivity and low TCR.
2. Description of the Prior Art
Hitherto, various investigations have been conducted regarding the method of manufacturing resistor pastes in order to improve the characteristics or stability of the compositions which are then used for manufacturing resistor. Also, resistors manufacturers have been experimenting with the use of intercompound metals as the material for making inorganic resistors, and there are many issued patents directed to the making of resistors using ruthenium oxides. Among such patents, U.S. Pat. No. 3,304,199 discloses a composition containing 2 to 70% by weight of RuO.sub.2, the rest being glass frit. However, when this composition is formed into a paste, printed and fired to form a resistor, and in spite of the fact that the glass frit in the composition usually contains PbO, pyrochlore-type compounds represented by a formula Pb.sub.2 Ru.sub.2 O.sub.6 can not be found in the fired resistor even in the examination through X-ray diffraction. U.S. Pat. No. 3,778,389 teaches an electric conductor consisting of a composite oxide composed of PbO, which compounds have been RuO.sub.2 and after blended together with glass frit and the addition of an organic binder, formed into a paste. Further, Japanese Pat. application No. 81296/1971 (Laid-open Print No. 8579/1972) discloses that a resistor containing Pb.sub.2 Ru.sub.2 O.sub.6 is produced when a resistor paste composed of a mixture consisting of lead ruthenate, or lead ruthenate and RuO.sub.2, and glass frit is fired.
Since the last-noted paste is obtained by first mixing ruthenium dioxide (or lead ruthenate) as a conductive component and glass frit as an inorganic binder, and then dispersing the mixture in an organic vehicle, the resistor formed by firing this mixture dose not have the conductive component and the glass frit in a uniform dispersion, and fluctuations in the initial resistance value of the resistor are likely to result. In addition, since the conductive portion and glass frit are present in a liberated state, the high voltage resistance properties are insufficient, and also the current noise level is unsatisfactory.
Meanwhile, U.S. Pat. No. 3,271,193 discloses the use of ruthenium resinates in combination with other resinate for glass forming such as lead resinate and silicon resinate. In this case, the dispersion of conductive component and inorganic binder is sufficiently uniform, but since the step of production of the resinate is complicated, the product lacks storage stability, and also the printing performance is insufficient. Therefore, the electric characteristics and the reliability as a resistor are insufficient.
The present inventors have conducted various studies and investigations with the object of obtaining a resistor paste which would overcome the above drawbacks and be excellent in high voltage resistance properties such that an improved resistor could be made therefrom. It was found that such a resistor could be obtained by firing a resistor paste which was manufactured by the method according to the invention as described hereinafter. Such a resistor has been found to have surprisingly excellent high voltage resistance properties as compared to prior-art resistors.
A further object of the present invention was to provide a method of manufacturing a resistor paste which would have less fluctuation in the initial resistance value, excellent resistance to high voltage, high resistivity, low TCR (temperature coefficient of resistivity) (value) and less current noise.